Active devices on a chip are generally spaced apart by regions known as field regions in which the isolation structures are formed. An alternative to the LOCal Oxidation of Silicon (LOCOS) process for isolation is known as trench isolation. Some trench process involve doped polysilicon fillers, such as when an ohmic contact is needed to be made between the polysilicon filler and the semiconductor substrate.
In one trench arrangement having doped polysilicon fillers, a two-step implant polysilicon filling process is used. A trench is formed in the substrate, such as by reactive ion etching (RIE), the trench is lined by a dielectric liner (e.g., thermal silicon oxide), and the lined trench is then filled by a polysilicon filler. The polysilicon filler material can then be doped, generally by ion implantation followed by a thermal implant activation step.